I agree with Brian.... add a pad on top of the neo air. Not sure where you are located, but I have heard Walmart sells blue foam pads much cheaper than elsewhere. I would be surprised if the REI trekker is warmer in real use than a neo air with a blue foam pad on top.

Also... be cognizant of where you are setting up your tent. If you set up on cold, hard ground (such as ice or granite) it will suck the warmth out of you. Look for soft ground

Also... eat some high calorie food before bed with a nice warm drink.

If all else fails fill your water bottle up with hot water and put it in the toe box of your sleeping bag (make sure it is well sealed).